What's this?(It's a lion.)为什么不能写there is?

what's this in English?It's a pen.为什么不能说是"this is a pen."?详细 what's this?It's a pen.为什么不能说是"this is a pen.我们老师说就是不能说this what is this ?It is a pen而不是It is pen.但为什么what's this? It's What is this?It is S.为什么回答不是 It is a S. What's this?It's a box.为什么回答中要用It's,而不用this is a box --what's this?--_____is a pen.为什么要填these?为什么不能填it? What's___(this)over there?It's a car. 选择题What's this?A.It's Z.B.It's red.C.This is ruler. 选择 What's this - ( )"A" A.It's B.It's an C.It's a D.This is l think it is sleeping.lt's a lion. this is a picture there"s a mountain in it A:What's this in English B:It's a jacket.A:What color is it